The invention relates to a keyboard pad comprising at least one depressable key which is resiliently supported in a frame member, the key being connected to the frame member by at least one spring element for returning the depressed key to its initial position after release, said members being made in one piece from a castable, resiliently yielding material.
Keyboards with resiliently supported keys for press buttons are used in many different fields in different types of apparatus and technical equipment. Such as keyboards for press-button operated telephone sets, calculators, data processing installations, etc.
Previously existing keyboards with resiliently supported keys traditionally have included a relatively large number of separate parts or members, with each of the individual, loose keys requiring its own separate spring for its resilient depression and return. The known constructions are further complicated in those cases where it is desired that the keys or buttons are to have a so-called "pressure point" characteristic, which means that the reaction force against depression increases gradually during the first part of the movement of the key, and thereafter is abruptly reduced when the "pressure point" is passed. For the achievement of a pressure point characteristic it is known to use a plastic disk having a dome elevation or "bubble" below each key, so that pressure point operation is achieved by snap action. However, with such an arrangement each key has very limited freedom of movement, and this is unsuitable in such cases where one wants a relatively large degree of movement combined with pressure point operation.
U.S. Pat. No. 3 668 356 discloses an actuator device with a press button which is connected to a base or frame member by way of connection elements in the form of two beam members of which each at one end is fixed in the frame member and at its other end through a hinge connection is connected to a respective rigid member which is in turn hingedly connected to a key actuating rod, said members being made in one piece by casting from a resilient material. This known device is of a relatively complicated construction and accordingly requires a correspondingly complicated mould to be manufactured by casting in one piece. Further, by depression of said actuating rod it is a presupposition that the angle between each fixed beam member and the associated rigid member must be less than 90.degree., which places a limitation on the travel of the actuating rod. Additionally, there is no effective return of the key when it is depressed beyond the pressure point, which is located at said angle.